Lennox MPB33CNM, MPB33CPM, MPB35CPM, MPB40CNM, MPB35CNM Installation Instructions Manual

INSTALLATION INSTRUCTIONS

éviter tout dommage matériel, toute blessure ou la mort.

WARNING /AVERTISSEMENT/AVISO

MPB B-Vent
Gas Fireplaces

MODELS

P/N 506015-05 Rev. D 04/2013

This manual is one of a set of two supporting this product.
Refer to P/N 506017-04 for Care and Operation Instructions.

Ce manuel est disponible en francais, simplement
en faire la demande. Numéro de la pièce 506223-45.

INSTALLER: Leave this manual with the appliance.
CONSUMER: Retain this manual for future reference.

INSTALLATEUR : Laissez cette notice avec l’appareil.
CONSOMMATEUR : Conservez cette notice pour
consultation ultérieure.

HOT GLASS WILL

CAUSE BURNS.

DO NOT TOUCH GLASS

UNTIL COOLED.

NEVER ALLOW CHILDREN

TO TOUCH GLASS.

UNE SURFACE VITRÉE CHAUDE

PEUT CAUSER DES BRÛLURES.

LAISSER REFROIDIR LA SURFACE

VITRÉE AVANT D'Y TOUCHER.

NE PERMETTEZ JAMAIS À UN ENFANT

DE TOUCHER LA SURFACE VITRÉE.

Decorative Product: Not for use as a heating appliance.

NOTICE: Fireplace is not to be operated by a thermostat.

MPB33CNM
MPB33CPM
MPB35CNM

MILLIVOLT:

MPB35CPM
MPB40CNM
MPB45CNM

OTL Report No. 116-F-36d-5

EL VIDRIO CALIENTE

CAUSARÁ QUEMADURAS.

USTED DEBE NUNCA

TOCAR EL VIDRIO CALIENTE.

LOS NIÑOS DEBEN NUNCA

TOCAR EL VIDRIO.

ELECTRONIC:

MPB33CNE
MPB35CNE

MPB40CNE
MPB45CNE

WARNING: If the information in these instructions
is not followed exactly, a fire or explosion may
result, causing property damage, personal injury,

AVERTISSEMENT : Assurez-vous de bien suivre les
instructions données dans cette notice pour réduire au
minimum le risque d’incindie ou d’explosion ou pour

or death.

- Do not store or use gasoline or other flammable
vapors and liquids in the vicinity of this or any other
appliance.

- WHAT TO DO IF YOU SMELL GAS:

• Do not try to light any appliance.

• Do not touch any electrical switch; do not use any
phone in your building.

• Immediately call your gas supplier from a
neighbor’s phone. Follow the gas supplier’s
instructions.

• If you cannot reach your gas supplier, call the fire
department.

- Installation and service must be performed by a
qualified installer, service agency or the gas supplier.

- Ne pas entreposer ni utilizer d’essence ni d’autres vapeurs
ou liquides inflammables dans le voisinage de cet appareil
ou de tout autre appareil.

- QUE FAIRE SI VOUS SENTEZ UNE ODEUR DE GAZ :

• Ne pas tenter d’allumer d’appareil.

• Ne touchez à aucan interrupteur. Ne pas vous servir des
téléphones se trouvant dans le bâtiment où vous trouvez.

• Appelez immédiatement votre fournisseur de gaz depuis
un voisin. Suivez les instructions du fournisseur.

• Si vous ne pouvez rejoindre le fournisseur de gaz,
appelez le service des incindies.

- L’installation et l’entretien doivent être assurés par un
installateur ou un service d’entretien qualifié ou par le
fournisseur de gaz.

LENNOX HEARTH PRODUCTS • MERIT PLUS® B-VENT GAS FIREPLACES (MPB33/35/40/45) • INSTALLATION INSTRUCTIONS

TABLE OF CONTENTS

Packaging .................................................... 2

Introduction ................................................. 2

General Information ..................................... 2

Requirements for the

Commonwealth of Massachusetts ............ 4

Cold Climate Insulation ................................ 4

Manufactured Housing ................................. 4

Location ........................................................5

Vent Termination Clearances ....................... 5

Appliance and Vent Clearances .................... 6

Pre-Installation Steps ................................... 7

Typical Installation Sequence ...................... 7

Detailed Installation Steps ............................ 7

Step 1. Framing ............................................ 7

Framing Specifications ................................ 8

Fireplace Specifications .............................. 9

Step 2. Routing Gas Line ............................. 9

Step 3. Installing Vent System ................... 10

Step 4. Field Wiring ................................... 11

Step 5. Wiring Optional

Forced Air Blower Kit .................... 12

Step 6. Connecting Gas Line ..................... 12

Step 7. Installing Optional Outside Air Kit ..13

Step 8. Verifying Appliance Operation ........... 14

Step 9. Installing Volcanic Stone, Glowing

Embers, and Logs ........................ 14

Step 10. Removing and

Installing the Glass Door ............. 19

Step 11. Burner Adjustments ..................... 19

Step 12. Testing Vent Operation ..................21

Step 13. Hood Installation .......................... 21

Step 14. Finishing Requirements ............... 21

Step 15. Attaching Safety-in-Operation

Warnings ............................ 22

Gas Conversion Kits ......................... 23

Please read and understand these
instructions before beginning your

installation.

2

PACKAGING

The assembled vented gas fireplace is pack­aged with:

• (1 set) Logs (packaged in a carton inside
the firebox).

• (1 bag) Volcanic Stone (included in the
firebox or bottom compartment).

• (1 bag) Glowing Embers (in bottom compart­ment).

• Literature Kit (envelope in bottom com­partment containing Care and Operation
Instructions, Installation Instructions,
Safety-In-Operation Warning Labels, War­ranty).

• (1) Hood (behind the top louver assembly).

INTRODUCTION

The Millivolt appliances have a millivolt gas
control valve with piezo ignition system. If any
optional accessories that will require electrical
power are to be installed, the electrical power
must be provided at the time of appliance in­stallation.

The Electronic appliances are designed to op­erate on natural or propane gas. An electronic
intermittent pilot ignition system provides safe,
efficient operation. External electrical power is
required to operate these units. In the event of a
power outage, four (4) "AA" batteries (in battery
holder) provide backup power for appliance
operation (excluding [optional] blower).

APPROVED VENT COMPONENTS

These vented gas fireplaces are designed for
residential applications. They must be installed
with approved Type-B, double wall vent pipe
systems and a listed vent termination routed
to the outside atmosphere. Use only the proper
size listed below.

REQUIRED PIPE DIAMETER:
MPB33 series: Requires 4" (102 mm)
MPB35 series: Requires 5" (127 mm)
MPB40 series: Requires 5" (127 mm)
MPB45 series: Requires 6" (152 mm)

WARNING

B-Vent appliances are not
designed to operate in negatively
pressured environments (pres­sure within the home is less than
pressures outside). Significant
negatively pressured environ­ments caused by weather, home
design, or other devices may
impact the operation of these
appliances. Negative pres­sures may result in poor flame
appearance, sooting, damage to
property and/or severe personal
injury. Do not operate these
appliances in negatively pres­sured environments.

GENERAL INFORMATION

WARNING

Young children should be care­fully supervised when they are
in the same room as the appli­ance. Toddlers, young children
and others may be susceptible
to accidental contact burns. A
physical barrier is recommended
if there are at risk individuals in
the house. To restrict access to
a fireplace or stove, install an
adjustable safety gate to keep
toddlers, young children and
other at risk individuals out of
the room and away from hot
surfaces.

AVERTISSEMENT

Les jeunes enfants devraient être
surveillés étroitement lorsqu’ils
se trouvent dans la même pièce
que l’appareil. Les tout petits,
les jeunes enfants ou les adultes
peuvent subir des brûlures s’ils
viennent en contact avec la sur­face chaude. Il est recommandé
d’installer une barrière physique
si des personnes à risques habi­tent la maison. Pour empêcher
l’accès à un foyer ou à un poêle,
installez une barrière de sécu­rité; cette mesure empêchera les
tout petits, les jeunes enfants et
toute autre personne à risque
d’avoir accès à la pièce et aux
surfaces chaudes.

Children and adults should be alerted to the
hazards of high surface temperature and
should stay away to avoid burns or clothing
ignition.

Les enfants et les adultes devraient être
informés des dangers que posent les
températures de surface élevées et se
tenir à distance afin d’éviter des brûlures
ou que leurs vêtements ne s’enflamment.

DO NOT ATTEMPT TO ALTER OR MODIFY
THE CONSTRUCTION OF THE APPLIANCE
OR ITS COMPONENTS. ANY MODIFICATION
OR ALTERATION MAY VOID THE WARRANTY,
CERTIFICATION AND LISTINGS OF THIS UNIT.

LENNOX HEARTH PRODUCTS • MERIT PLUS® B-VENT GAS FIREPLACES (MPB33/35/40/45) • INSTALLATION INSTRUCTIONS

WARNING

Improper installation, adjust­ment, alteration, service or
maintenance can cause injury
or property damage. Refer to
this manual. For assistance or
additional information consult
a qualified installer, service
agency or the gas supplier.

WARNING

Failure to comply with these in­stallation instructions will result
in an improperly installed and
operating appliance, voiding its
warranty. Any change to this appli­ance and/or its operating controls
is dangerous.

WARNING

Clothing or other flammable
material should not be placed
on or near the appliance.

AVERTISSEMENT

On ne devrait pas placer de
vêtements ni d’autres matières
inflammables sur l’appareil ni à
proximité.

WARNING

Any safety screen or guard re­moved for servicing the appli­ance must be replaced prior to
operating the appliance.

AVERTISSEMENT

Tout écran ou protecteur retiré
pour permettre l’entretien de
l’appareil doit être remis en
place avant de mettre l’appareil
en marche.

WARNING

Improper installation or use of
this appliance can cause serious
injury or death from fire, burns,
explosion or carbon monoxide
poisoning.

WARNING

Failure to position the parts in
accordance with these diagrams
or failure to use only parts
specifically approved with this
appliance may result in property
damage or personal injury.

AVERTISSEMENT

Risque de dommages ou de
blessures si les pièces ne sont
pas installées conformément à
ces schémas et ou si des pièces
autres que celles spécifiquement
approuvées avec cet appareil sont
utilisées.

Installation and repair should be done by
a qualified service person. The appliance
should be inspected before use and at least
annually by a professional service person.
More frequent cleaning may be required due
to excessive lint from carpeting, bedding
material, etcetera. It is imperative that control
compartments, burners and circulating air
passageways of the appliance be kept clean.

L’installation et la réparation devrait
être confiées à un technicien qualifié.
L’appareil devrait faire l’objet d’une
inspection par un technicien professionnel
avant d’être utilisé et au moins une fois
l’an par la suite. Des nettoyages plus
fréquents peuvent être nécessaires si les
tapis, la literie, et cetera produisent une
quantité importante de pous-sière. Il est
essentiel que les compartiments abritant
les commandes, les brûleurs et les
conduits de circulation d’air de l’appareil
soient tenus propres.

Do not use this appliance if any part has
been under water. Immediately call a
qualified service technician to inspect the
appliance and to replace any part of the
control system and any gas control which
has been under water.

Ne pas utiliser cet appareil s’il a été
plongé, même partiellement, dans
l’eau. Appeler un technicien qualifié
pour inspecter l’appareil et remplacer
toute partie du système de commande
et toute commande qui a été plongée
dans l’eau.

Only trim kit(s) supplied by the manufacturer
shall be used in the installation of this
appliance.

Seules les trousses de garniture fournies
par le fabricant doivent être utilisées pour
l’installation de cet appareil.

These appliances comply with National
Safety Standards and are tested and listed
by OMNI-Test Laboratories, Inc. (Report No.
116-F-36d-5) to ANSI Z21.50b-2009 (in Canada,
CSA 2.22b-2009), and CAN/CGA-2.17-M91
(R2009) in both USA and Canada, as vented
gas fireplaces.

Both millivolt and electronic versions of these
appliances may be used in bedrooms only
when the room is an "unconfined space" as
defined by the National Fuel Gas Code. Use
in bedrooms may not be allowed by your local
building codes. You should obtain prior ap­proval from the Authority having jurisdiction
prior to installation.

MISC. CODES / STANDARDS

The Installation must conform to local codes or, in
the absence of local codes, with the National Fuel
Gas Code, ANSI Z223.1 / NFPA 54 - latest edition
(In Canada, the current CAN/CGA-B149.1 installation
code).The appliance, when installed, must be
electrically grounded and wired in accordance with
local codes or, in the absence of local codes, with
the National Electrical Code, ANSI/NFPA 70 - latest

edition, or the Canadian Electrical Code, CSA C22.1

- latest edition.

Provide adequate clearances around air
openings and adequate accessibility clearance for
service and proper operation. Never obstruct the
front or back openings of the appliance.

These appliances are designed to operate on
natural or propane gas only. The use of other
fuels or combination of fuels will degrade
the performance of this system and may be
dangerous.

These fireplaces are designed as decorative
appliances and are not intended for use as
area heaters. They must not be equipped
with wall thermostats or remote controls with

thermostat functions.
OUTSIDE COMBUSTION AIR HOOK UP

These appliances are equipped with an
integral combustion air door and actuator arm.
Combustion air kits are optional. Install as shown
in Step 7 on Page 13.

These appliances must not be connected to a
chimney or flue serving a separate solid fuel
burning appliance.

Both millivolt and electronic systems can be
operated during a power outage, and feature
manually operated hi-low flame control. The BTU
Input for these appliances is shown in Table 1.

Natural Gas Propane Gas

Model Input Rate

MPB33 13,500 to

MPB35 16,000 to

MPB40 24,000 to

MPB45 24,750 to

Table 1 - BTU Input Ratings

(BTU/HR)

17,500

20,000

30,000

31,000

Input Rate

BTU/HR)

13,500 to

17,500

16,500 to

20,000

22,300 to

28,000

23,000 to

29,000

3

LENNOX HEARTH PRODUCTS • MERIT PLUS® B-VENT GAS FIREPLACES (MPB33/35/40/45) • INSTALLATION INSTRUCTIONS

GAS PRESSURE - ALL MODELS

Tables 2 and 3 show the appliances' inlet and
manifold gas pressure requirements:

Fuel # Minimum Maximum

Natural Gas 4.5" WC

Propane 11.0" WC

(1.12 kPa)

(2.74 kPa)

10.5" WC

(2.62 kPa)

13.0" WC

(3.24 kPa)

Table 2 - Inlet Gas Supply Pressure

Fuel # Low High

Natural Gas 2.2" WC

Propane 6.3" WC

(0.55 kPa)

(1.57 kPa)

3.5" WC

(0.87 kPa)

10.0" WC

(2.49 kPa)

Table 3 - Manifold Gas Supply Pressure

Test gauge connections are provided on the
front of the millivolt and electronic gas control
valve (identified IN for the inlet and OUT for the
manifold side). The control valves have a 3/8"
(10 mm) NPT thread inlet and outlet side of the
valve (refer to Figures 1 and 2).

Propane tanks are at pressures that will cause
damage to valve components. Verify that the
tanks have step down regulators to reduce the
pressure to safe levels.

The appliance and its appliance main gas
valve must be disconnected from the gas
supply piping system during any pressure
testing of that system at test pressures in
excess of 1/2 psi (3.5 kPa).
The appliance must be isolated from the gas
supply piping system by closing its equipment
shutoff valve during any pressure testing of
the gas supply piping system at test pres­sures equal to or less than 1/2 psi (3.5 kPa).

ORIFICE SIZES - SEA LEVEL TO HIGH
ALTITUDE (ALL MODELS)

These appliances are tested and approved for
installation at elevations of 0 - 4500 ft (0 - 1372
m) above sea level using the standard burner
orifice sizes (marked with an "*" in Table 4).
For elevations above 4500 ft, contact your gas
supplier or qualified service technician.

Deration - At higher elevations, the amount
of BTU fuel value delivered must be reduced
by either:

• Using gas that has been derated by the gas

company.

Install the appliance according to the regulations
of the local authorities having jurisdiction and,
in the USA, the National Fuel Gas Code NFPA
54 - latest edition / ANSI Z223.1 or, in Canada,
the CAN/CGA-B149.1 - latest edition.

Flame breadth, height and width will diminish
4% for every 1,000 feet of altitude. Gas Valve

Diagrams

. See Figure 1 for millivolt models

and Figure 2 for electronic models.

In Canada - CAN/CGA-2.17-M91 (R2009)
(high altitude): THE CONVERSION SHALL
BE CARRIED OUT BY A MANUFACTUR­ER’S AUTHORIZED REPRESENTATIVE,
IN ACCORDANCE WITH THE REQUIRE­MENTS OF THE MANUFACTURER, PRO­VINCIAL OR TERRITORIAL AUTHORITIES
HAVING JURISDICTION AND IN ACCOR­DANCE WITH THE REQUIREMENTS OF
THE CAN/CGA-B149.1 OR CAN/CGA­B149.2 INSTALLATION CODES.

Main Gas Control Knob

OFF/PILOT/ON

N

O

T

O

it

L

I

P

O

F

F

OUT

IN

Manifold Pressure Tap

Inlet Pressure Tap

Pilot Adjustment

I

P

W

O

L

H

I

HI/LO Variable
Flame Height
Adjustment

Screw

T

O

L

HTPTHTPT

Figure 1 - SIT Millivolt Gas Valve

(from DFC Wire Harness)

Inlet (IN) Test Port

Manifold (OUT) Test Port

Orange Wire

(from DFC Wire

Harness)

Green Wire

Burner Orifice Sizes

Elevation 0-4500 feet ( 0-1372 meters)

Model

MPB33

MPB35

MPB40

MPB45

Table 4

Nat.Gas

drill size (inches)

#47 (0.0785")*

99K74 •

#44 (0.086")*

60J80 •

#38 (0.102")*

99K76 •

#37 (0.104")*

24M10 •

* Standard size installed at factory

• Part /Cat. Number

Propane

drill size (inches)

(0.048")*

99K78 •

#55 (0.052")*

19L52 •

(0.062")*

21L01 •

#52 (0.0635")*

37G00 •

REQUIREMENTS FOR THE COMMON­WEALTH OF MASSACHUSETTS

These fireplaces are approved for installation in
the US state of Massachusetts if the following
additional requirements are met:

• Install this appliance in accordance with

Massachusetts Rules and Regulations 248
C.M.R.

• Installation and repair must be done by a

plumber or gas fitter licensed in the Com­monwealth of Massachusetts.

• The exible gas line connector used shall

not exceed 36 inches (92 centimeters) in
length.

• The individual manual shut-off must be a

T-handle type valve.

Cold Climate Insulation

For cold climate installations, seal all cracks
around your appliance with noncombustible
material and wherever cold air could enter
the room. It is especially important to insulate
outside chase cavity between studs and under
floor on which appliance rests, if floor is above
ground level. Gas line holes and other openings
should be caulked or stuffed with unfaced
fiberglass insulation.

Hi/Lo Flame
Control Knob

• Changing the burner orice to a smaller size

as regulated by the local authorities having
jurisdiction and by the (USA) National Fuel
Gas Code NFPA 54/ANSI Z223.1 - latest
edition or, in Canada, the CAN/CGA-B149.1
codes - latest edition.

4

Main Gas Inlet

3/8" NPT

Yellow Ground Wire
(from DFC Wire Harness)

Figure 2 - SIT Electronic Gas Valve

NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.

LENNOX HEARTH PRODUCTS • MERIT PLUS® B-VENT GAS FIREPLACES (MPB33/35/40/45) • INSTALLATION INSTRUCTIONS

If the fireplace is being installed on a cement
slab in cold climates, a sheet of plywood or
other raised platform can be placed underneath
to prevent conduction of cold transferring to
the fireplace and into the room. It also helps to
sheetrock inside surfaces and tape for maximum
air tightness and caulk firestops.

MANUFACTURED HOUSING

B-Vent Fireplaces are not approved for use in
OEM or aftermarket manufactured housing built
to HUD standards.

LOCATION

In selecting the location, the aesthetic and
functional use of the appliance are primary
concerns. However, vent system routing to
the exterior and access to the fuel supply are
also important.

Due to high temperatures, the appliance
should be located out of traffic and away from
furniture and draperies (Figure 3).

En raison des températures élevées,
l’appareil devrait être installé dans un
endroit où il y a peu de circulation et loin
du mobilier et des tentures (Figure 3).

The location should also be free of electrical,
plumbing or other heating/air conditioning
ducting.

Be aware that this is a heat producing ap­pliance. Objects placed above the unit are
exposed to elevated temperatures.

Do not insulate the space between the ap­pliance and the area above it (see Figure 10

on Page 8).
The appliance must be mounted on a fully

supported base extending the full width
and depth of the unit. The appliance may be
located on or near conventional construction
materials. However, if installed on combustible
materials, such as carpeting, vinyl tile or other
combustible material other than wood flooring,
the appliance shall be installed on a metal or
wood panel extending the full width and depth
of the appliance

VENT TERMINATION CLEARANCES
Gas Vent Rule - Gas vent caps are not per-

mitted within 8 feet (2.4 mm) of a vertical
wall or similar obstruction. Gas vent caps
that are located 8' or more from a portion
of a building which extends at an angle
greater than 45° upward from the horizontal
may terminate in accordance with Figure 4,
provided that in no case shall any discharge
opening on the cap be less than 2' (610 mm)
horizontally from the roof surface (National
Fuel Gas Code ANSI Z223.1 (NFPA 54) Gas
Vent Termination) (CAN/CGA B149.1).

MULTIPLE TERMINATIONS

These appliances may vent adjacent to and at
the same level with any other gas appliances
(including direct-vent appliances) provided that
there is at least 2 ft. (0.6m) between the proximal
edges of the vent caps. These appliances may
be vented adjacent to a chimney vent servicing
a solid fuel fireplace provided the B-vent cap
is at least 2 ft. (0.6m) away from the nearest
point of the chimney opening.

Vertical
Venting

Shown with Outside Air Kit
installed (model FOAK-4 or

FOAK-4LD)

When the unit is installed with one side flush with a
wall, the wall on the other side of the unit must not
extend beyond the front edge of the unit.

Figure 3 - Typical Installations

X

12

Roof Pitch is X/12

Minimum Height from Roof to
Lowest Discharge Opening

1“ (25 mm)
Minimum

Figure 4 - Vertical Vent Termination

Clearances

2 ft.

(0.6m)

Minimum

Figure 5 - Multiple Terminations

NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.

Offset

Venting

Termination Heights For Vents

Above Flat Or Sloped Roofs
Ref. NFPA 54 / ANSI Z223.1

Roof Pitch Feet Meters

Flat to 6/12 1.0 0.3
6/12 to 7/12 1.25 0.38
7/12 to 8/12 1.5 0.46
8/12 to 9/12 2.0 0.61

9/12 to 10/12 2.5 0.76
10/12 to 11/12 3.25 0.99
11/12 to 12/12 4.0 1.22
12/12 to 14/12 5.0 1.52
14/12 to 16/12 6.0 1.83
16/12 to 18/12 7.0 2.13
18/12 to 20/12 7.5 2.29
20/12 to 21/12 8.0 2.44

5

12 (305) MANTEL

10 (254) MANTEL

8 (203) MANTEL

6 (152) MANTEL

4 (102) MANTEL

4

(102)

14

(356)

12

(305)

10

(254)

2 (51) MANTEL

TOP OF
APPLIANCE

6

(152)

NOTE - Hood shown as positioned in louvered
front model. The hood position in the flush
faced front model is lower than shown.

8

(203)

MANTEL CLEARANCES

Inches (mm)

LENNOX HEARTH PRODUCTS • MERIT PLUS® B-VENT GAS FIREPLACES (MPB33/35/40/45) • INSTALLATION INSTRUCTIONS

APPLIANCE AND VENT CLEARANCES

MINIMUM CLEARANCES TO COMBUSTIBLES

The appliance is approved with zero
clearance to combustible materials on
all sides. Refer to Table 5 for minimum
clearance values. For typical installations,
see Figure 3 on Page 5.

Minimum Clearances

Back 1/2" (13 mm)

Sides 1/2" (13 mm)

Top Spacers 3" (76 mm)

Floor 0" (0 mm)

Bottom of
Appliance
To Ceiling

Vent 1" (25.4 mm)

Front 3' (0.9 m)

0 (0) from Spacers or Dimples

0 (0) from Spacers or Dimples

0" (0 mm)

with standoff(s) in vertical

position

64" (1626 mm)

SERVICE CLEARANCES

Table 5

NOTE: 3" (75 mm) minimum clearance is

required above any inclined vent component.

1" minimum clearance is required to the sides

of vertical vent.

Hearth Extension - A hearth extension is not

required with this appliance. If a hearth exten­sion is used, do not block the lower control
compartment door. Any hearth extension used
is for appearance only and does not have to
conform to standard hearth extension instal­lation requirements.

WALL FINISHES / SURROUNDS / MANTELS

NOTE: Combustible wall finish materials and/
or surround materials must not be allowed to
encroach the area defined by the appliance
front face (black sheet metal). Never allow

combustible materials to be positioned in
front of or overlapping the appliance face.

Refer to Figure 36 on Page 21 for clearance
recommendations and requirements.

Figures 6 and 7 illustrate the areas surrounding
the fireplace where clearances are an issue. The
outer edge of the metal trim on only one side
of the fireplace may abutt a perpendicular wall.
For this type of installation, the other side of the
fireplace must be a flat wall to allow for proper
air flow and burner operation.

Combustible materials may project beyond one
or both sides of the fireplace opening when
these materials are kept within the "Safe Zone"
illustrated in Figure 6.

Top View of

Fireplace

At 0 in. minimum
side wall clearance,
one combustible
wall can project to
any length.

Figure 6 - Clearance References

Non-combustible materials, such as surrounds
and other appliance trim, may be installed on the
appliance face with these exceptions:

They must not cover any portion of the removable
glass panel, louvers, or control compartment.

Vertical installation clearances to combustible
mantels vary according to the depth of the
mantel (see Figure 7). Mantels constructed of
non-combustible materials may be installed
at any height above the appliance opening;
however, do not allow anything to hang below
the fireplace hood.

Minimum clearance requirements include any
projections such as shelves, window sills,
mantels, etc. above the appliance.

NOTE: We recommend the use of high
temperature paint (rated 175 °F, or higher)
on the underside of the mantel.

Mantel Leg,

Trim, or Wall

3 1/2 in.

(89 mm)

45

o

Combustible materials
may project beyond
either side of the
fireplace opening as
long as they are kept
within the shaded
“Safe Zone” area.

0” Clearance
to Combustible
Side Wall

Bottom of Fireplace

Figure 7 - Wall Clearances

Ceiling

64"

(1626 mm)

6

Figure 8 - Minimum Mantel Clearances

NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.

LENNOX HEARTH PRODUCTS • MERIT PLUS® B-VENT GAS FIREPLACES (MPB33/35/40/45) • INSTALLATION INSTRUCTIONS

Anchor
Ta b

Note: The nailing flanges, combustible members
and screw heads located in areas directly adjacent
to the nailing flanges, are EXEMPT from the 1/2”
clearance to combustible requirements for the
firebox outer wrapper.

Combustible framing may be

in

direct contact with the nailing flanges and may
be located closer than 1/2” from screw heads and
the firebox wrapper in areas adjacent to the nailing
flanges. Frame the opening to the exact dimensions
specified in the framing details of this manual.

Side

Framing

Unit Nailing Flange

(No clearance to

combustible

framing is required)

Left Side Front Corner of Fireplace Shown

(Right Side Requirements the Same)

PRE-INSTALLATION STEPS

The appliance is shipped with all gas controls
and components installed and pre-wired.

1. Before installing the appliance, follow these

steps:

2. Remove the shipping carton.

3. Remove the shipping pad, exposing the front

glass door.

4. Open the spring latch securing the glass

door (under the firebox floor). Remove the
door by tilting it outward at the bottom and
lifting it up. Set the door aside, taking care
to protect it from inadvertent damage. See

Removing the Glass Enclosure Panel on Page

19.

5. Remove the log set from the firebox. Handle

logs carefully to prevent breakage.

6. Remove the embers and volcanic stone from

the control compartment.

TYPICAL INSTALLATION SEQUENCE

The typical sequence of installation is outlined
below; however, each installation is unique and
may result in variations to the steps described.
See the pages referenced in the following steps
for detailed procedures.

Step 1. FRAMING (Page 7): Construct the
appliance framing. Position the appliance within
the framing and secure with nailing flanges and
floor anchor tabs.

Bend out the appropriate nailing flanges for
the drywall/finish material to be used. Nailing
flanges are provided for flush framing, 1/2" and
5/8" framing depths (see Figure 8).

Step 2. ROUTING GAS LINE (Page 9): Route
gas supply line to appliance location.

Step 3. INSTALLING VENT SYSTEM (Page 10):
Install the vent system and exterior termination.

Step 4. FIELD WIRING (Page 11).

a. Millivolt Appliances - Install the operating

control switch (not factory provided). If
installing the optional forced air circulating
blower, bring in electrical service line.

b. Electronic Appliances - Field wire and
install operating control switch.

Step 5. WIRING - OPTIONAL FORCED AIR
BLOWER KIT (Page 12).

Step 6. CONNECTING GAS LINE (Page 12):

Step 7. INSTALLING OPTIONAL OUTSIDE AIR

Make connection to gas supply.

KIT (Page 13)
Step 8. VERIFYING APPLIANCE OPERATION

(Page 14).

Step 9. INSTALLING VOLCANIC STONE,
GLOWING EMBERS, AND LOGS (Page 14).

Step 10. REMOVING AND INSTALLING THE
GLASS DOOR (Page 19).

Step 11. BURNER ADJUSTMENTS (Page 19):

Adjust burner primary air shutter to achieve
proper flame appearance.

Step 12. TESTING VENT OPERATION (Page 21)

Vent operation test and (safety limit) switch
operation.

Step 13. HOOD INSTALLATION (Page 21).
Step 14. FINISHING REQUIREMENTS (Page 21)
Step 15. ATTACHING SAFETY-IN-OPERATION

WARNINGS (Page 22).

DETAILED INSTALLATION STEPS
STEP 1. FRAMING

Frame the appliance as illustrated in Figure 11
on Page 8. All framing details must allow for
a minimum clearance to combustible framing
members as shown in the table on Page 8.

If the appliance is to be elevated above floor
level, a solid continuous platform must be
constructed below the appliance.

NOTE: The framed depth, 16" (406 mm) from
a framed wall, must always be measured from
a finished surface. If a wall covering such as
drywall is to be attached to the rear wall, then
the 16" (406 mm) must be measured from the
drywall surface. It is important that this dimen­sion be exact.

Headers may be in direct contact with the
appliance top standoff spacers, but must not

be supported by them or notched to fit around
them. All construction above the appliance

must be self-supporting. DO NOT use the

appliance for structural support.

Secure the fireplace to the side framing members
using the unit’s nailing flanges - one top and
bottom on each side of the fireplace front (see
Figure 9). Use 8d nails or their equivalent.

NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.

FLOOR NAILING TABS

Fireplace may be anchored to floor. Bend down
two anchor tabs (one on each side) located
at the base of the fireplace and secure to the
floor by nailing with 8d nails or equivalent (see

Figure 10).

Figure 9 - Unit Secured to Framing by

Nailing Flange

Figure 10 - Floor Anchor Tabs

NOTE: Some units only have one anchor tab
on each side.

7

LENNOX HEARTH PRODUCTS • MERIT PLUS® B-VENT GAS FIREPLACES (MPB33/35/40/45) • INSTALLATION INSTRUCTIONS

HH

. o N l e d o M

A

t i n U

e z i S

A

g n i m a r F

e z i S

BCDEFGHJ K

. n i5 38 / 1 -5 34 / 1 -5 34 / 1 -9 18 / 5 - 9 17 52 / 1 -4 / 3 - 8 26 14 6 1 / 9 - 68 / 5 - 0 4

m m2 9 85 9 85 9 83 8 48 9 40 6 4 10 3 76 0 42 0 17 6 12 3 0 1

. n i8/ 1 - 0 44 / 1 - 0 44 / 1 - 0 44 28 / 5 - 4 26 1 / 3 1 - 1 66 1 / 1 - 0 36 14 6 1 / 9 - 62 3 / 1 1 - 3 4

m m9 1 0 12 2 0 12 2 0 10 1 65 2 60 7 5 19 7 76 0 42 0 17 6 11 0 1 1

. n i8 / 1 - 0 44 / 1 - 5 44 / 1 - 0 44 28 / 5 - 9 28 / 3 - 6 66 1 / 3 - 3 36 14 6 1 / 9 - 66 1 / 5 1 - 6 4

m m6 4 1 19 4 1 12 2 0 10 1 62 5 76 8 6 13 4 86 0 42 0 17 6 12 9 1 1

MPB33

MPB35

MPB40

MPB45

in.

mm

845

842

33-1/4

845

33-1/4

546

21-1/2

286

11-1/4

1232

48-1/2

616

24-1/4

330

13

102

4

103

4-1/16

872

34-5/16 33-1/8

12-3/4

14-11/16

17-3/16

437

373

324

1146

45-1/8

24-7/8

29-7/8

34-7/8

886

759

632

30-11/16

7-1/16

7-1/16

7-1/16

179

179

179

Back Wall of Chase/Enclosure

*Optional FOAK

Outside

Air Kit

Including Finishing Materials

C

if any

B

Fireplace Framing

K

Corner Installation

Header

A

Back Wall of Chase/Enclosure

Including Finishing Materials

D

C

A
E

if any

G

Rough

Framing Face

(Unfinished Shown)

J

A

Rough Framing Face

(Unfinished Shown)

Outside Chase

Back Wall of Chase/Enclosure
Including Finishing Materials

C

F

A

Inside Chase

if any

G

G

Rough

Framing Face

(Unfinished Shown)

All framing dimensions calculated for 1/2" dry wall at the appliance face. If sheathing the chase or finishing with other thickness materials,
calculations will need to be made.
* Outside air kit - FOAK (without adaptor). See Figure 23 on Page 14.

8

Figure 11 - Framing Specifications

NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.